In many applications radio devices alert a user of the device when a call has been received. Such devices generally produce an audible alerting signal which can be heard by the user. However, an audible signal may produce a disturbance in some places where there is a low ambient noise level, and may not be heard in other places where there is a high ambient noise level. A manual sound level control can be provided to change the level of the sound for different situations. However, such a manual control is objectionable as the level control may be set to a level such that the audible alerting signal produces a disturbance or is not heard.
To eliminate the use of an audible alerting signal in places where this is objectionable, some radio devices use a silent alert signal, such as that produced by a vibrating device, so that the user of the radio device feels, rather than hears, the alerting signal. This is objectionable as it is only effective when the radio device is worn on the body of the user.
Some radio devices may provide both an audible and a silent alert. A manual control can be provided to alternatively select between the audible alert and the silent alert for different situations. However, such a control is objectionable as the user may forget that the audible alert was selected so the audible alert signal produces a disturbance or is not heard, or the user may forget that the silent alert was selected so the silent alert goes undetected to the user when the radio device is not worn on the body of the user.
Accordingly, there is a need to insure that the user of a radio device will be alerted when a call has been received in a wide range of ambient noise levels and distances of the radio device relative to the user's body.